1. Field of the Invention
The present invention relates generally to communication control depending on communication conditions, which includes a plurality of interfaces such as an interface supporting WLAN (Wireless Local Area Network) and an interface supporting a central network, and more particularly, to a communication apparatus, network apparatus, communication system, communication method communication program, and recording medium that select the interface for detour call reception.
2. Description of the Related Art
Among standards such as a cellular (cellular communication system) network and WLAN relating to mobile communication such as portable telephones, the cellular network includes, for example, CDMA (Code Division Multiple Access)-2000, W-CDMA (Wideband Code Division Multiple Access) and GSM (Global System for Mobile Communications), and the WLAN includes, for example, IEEE (Institute of Electrical and Electronic Engineers) 802.11g, WiMAX (Worldwide Interoperability for Microwave Access). A line interface is needed to support each network and a communication terminal apparatus supporting the both network needs two line interfaces. Therefore, the communication terminal apparatus with the line interfaces supporting the networks is referred to as a “DUAL terminal apparatus” for convenience.
With regard to the mobile communication across a plurality of networks such as the cellular network and WLAN, Published Japanese Translation of PCT Application No. 2002-501353 discloses a communication system that communicates using ground communication lines for short-distance calls and using a wireless access communication apparatus for long-distance calls (paragraph No. 0022 and FIG. 1). Japanese Patent Application Laid-Open Publication No. 2005-33707 discloses a communication system that can select a fixed mode for communicating only within a fixed zone, a mobile mode for communicating while moving, and a connection form such as a portable terminal communication network, PHS (Personal Handyphone System) communication network, and a cable communication network in response to information of the area where an excellent communication state for a communication terminal can be secured and information of communication that can secure the excellent communication state among a plurality of connection forms (abstract, FIG. 1). Published Japanese Translation of PCT Application No. 2005-531984 discloses that a portable telephone network can use the data signal connection between a WLAN and the portable telephone network to call a user device through a wireless channel of the WLAN if the user device is idle for a wireless telephone network and active for the WLAN and that the WLAN and the portable telephone network can use the data signal connection between the WLAN and the portable telephone network to call the user device if the user device is idle for the wireless telephone network and the WLAN (paragraph Nos. 0023, 0034, FIGS. 1, 4, and 7).
When a wireless communication apparatus is powered off in the communication system described in Published Japanese Translation of PCT Application No. 2002-501353, registration of subscriber identifiers is cancelled in a switchboard, and since registration in a center is also deleted because of powering off, an internal switchboard does not receive detour calls through PSTN (Public Switched Telephone Network). In Japanese Patent Application Laid-Open Publication No. 2005-33707, a terminal apparatus merely transmits a declaration signal indicating a connection form (mobile mode or fixed mode (local mode such as WLAN and fixed line)) and a network state is comprehended on the network side and supplied to the terminal apparatus. Published Japanese Translation of PCT Application No. 2005-531984 merely discloses that automatic transfer is performed to the connection setting side of the interface supporting the portable telephone network and WLAN.
By the way, wasteful power consumption is generated by supplying electric power to each interface of a communication apparatus including a plurality of interfaces and a battery life is greatly affected in the case of a portable device powered by a battery. Although cutting off power to inactive interfaces contributes to suppression of power consumption and increase of the battery life in the case of a portable device, if power supply to inactive interfaces is stopped, communication cannot be performed through the interfaces and a degree of freedom of communication is hindered.
In the case of wireless communication, the field intensity affects communication quality and if the field intensity is insufficient, communication becomes impossible. In a communication apparatus including a plurality of interfaces supporting a plurality of networks such as the cellular network and WLAN, a network can be selected depending on the field intensity, and communication breakdown due to reduction of the field intensity can advantageously be avoided.
Communication conditions such as usage fees are different in a plurality of networks such as the cellular network and WLAN, which gives users a degree of freedom of selection as needed.
In association with the power supply cutoff, field intensity, and communication conditions of such interfaces, it is desirable to achieve a convenient communication environment without deteriorating a degree of freedom of communication. Published Japanese Translation of PCT Application Nos. 2002-501353, 2005-531984, and Japanese Patent Application Laid-Open Publication No. 2005-33707 do not disclose and indicate such problems and do not disclose and indicate the solutions thereof.